Bosch Pro Tankless GWH-450-ES Series User manual

GWH 450 ES
Temperature Modulated with Electronic Ignition - Normal duty
Suitable for recirculating potable water only
GWH-450-ES-N - Natural Gas
GWH-450-ES-L - Liquefied Petroleum (LP) Gas
6 720 607 915 US (06.10) JS
Warning: If the information in this manual is not
followed exactly, a fire or explosion may result
causing property damage, personal injury or death.
Do not store or use gasoline or other flammable
vapor and liquids in the vicinity of this or any other
appliance.
Improper installation, adjustment, alteration,
service or maintenance can cause injury or
property damage. Refer to this manual. For
assistance or additional information consult a
qualified installer, service agency or the gas
supplier.
In the Commonwealth of Massachusetts this
product must be installed by a licensed plumber or
gas fitter.
Upon completion of the installation, these
instructions should be handed to the user of the
appliance for future reference.
What to do if you smell gas
• Close gas valve. Open windows.
• Do not try to operate any appliance.
• Do not touch any electrical switch; do not use any
phone in your building
• Immediately call your gas supplier from a neighbor’s
phone. Follow the gas supplier’s instructions.
• If you cannot reach your gas supplier, call the fire
department.
• Installation and service must be performed by a qual-
ified installer, service agency or the gas supplier.

6 720 607 915
2
Index
Index
1 Warning 2
2 Appliance details 4
2.1 Features 4
2.2 GWH-450-ES Specifications (Technical data) 4
2.3 Unpacking the GWH-450-ES heater 5
2.4 General rules to follow for safe operation 6
2.5 Cascading function 6
2.6 Dimensions and minimum installation clearances 7
2.7 Applications 8
3 Installation instructions 9
3.1 Introduction 9
3.2 Proper location for installing your water heater 9
3.3 Water heater placement and clearances 9
3.4 Mounting installation 9
3.5 Combustion air requirements 10
3.6 Venting 11
3.6.1 Venting options 14
3.7 Gas piping & connections 16
3.8 Measuring gas pressure 18
3.9 Water connections 19
3.10 Electrical connections 19
4 Operating instructions 20
4.1 For your safety read before operating your water
heater 20
4.2 Startup instructions 20
4.3 Power 21
4.4 Water temperature 21
4.5 Power adjustment 21
4.6 Freeze prevention 21
4.7 Electrical diagram 22
5 Maintenance and service 23
6 Troubleshooting 24
7 GWH-450-ES Functional scheme 26
8 Interior components diagram and parts list 27
8.1 Interior components 27
8.2 Components diagram 28
8.3 Parts list 29
9 Protecting the environment 30
10 Fifteen Year Limited Warranty 31
1 Warning
For your safety
Do not store or use gasoline or other flammable,
combustible or corrosive vapors and liquids in the
vicinity of this or any other appliance.
Warning: Carefully plan where you
install the heater. Correct combustion
air supply and flue pipe installation are
very important. If a gas appliance is not
installed correctly, fatal accidents can
result from lack of air, carbon monoxide
poisoning or fire.
Warning: Exhaust gas must be vented
to outside using proper vent material
suitable for category III vent systems
and temperatures up to 480°F. Vent
and combustion air connector piping
must be sealed gas-tight to prevent
possibility of flue gas spillage, carbon
monoxide emissions and risk of fire,
resulting in severe personal injury or
death.
Warning: Place the recirculating water
heater in a location where water leaks
will do NO DAMAGE to adjacent areas
or lower floors.
Warning: Field wiring connections and
electrical grounding must comply with
local codes, or in the absence of local
codes, with the latest edition of the
National Electric Code, ANSI/NFPA 70,
or in Canada, all electrical wiring must
comply with the local codes and the
Canadian Electrical Code, CSA C22.1
Part 1.
Warning: Shock hazard line voltage is
present. Before servicing the
recirculating water heater, turn off the
electrical power to the recirculating
water heater at the main disconnect or
circuit breaker. Failure to do so could
result in severe personal injury or death.

6 720 607 915
Warning
3
FCC:
This device complies with Part 15 of the FCC rules.
Operation is subject to the following two conditions: (1)
This device may not cause harmful interference, and (2)
this device must accept any interference received,
including interference that may cause undesired
operation.
Fig. 1
Warning: The recirculating water
heater must be disconnected from the
gas supply piping system during any
pressure testing of that system at test
pressures equal to or more than 0.5
psig.
Caution: Any changes or
modifications not expressly approved
by the party responsible for compliance
could void the user’s authority to
operate the equipment.

6 720 607 915
4
Appliance details
2 Appliance details
2.1 Features
Parts
• Sealed combustion burner.
Safety
• Ionization flame sensor
• Over temperature protection.
High quality materials for long working life
• Copper heat exchanger
• Compact space saver: mounts on a wall with
supplied bracket.
Features
• LED to display temperatures, burner operation and
diagnostic error codes.
• On/Off button and separate temperature controls for
domestic and heating
• Reset button
• Failure code for diagnostics and repair
• Freeze prevention cycle.
Accessories
• Horizontal vent kit
• Pump manifold
• 12 kOhm DHW thermistor.
2.2 GWH-450-ES Specifications
(Technical data)
Approved in US/Canada
Capacity
GWH450 Maximum flow rate: 4.5 GPM (17 l/min) at a
45°F (25°C) rise.
Maximum output
GWH450 - 98,400 Btu/h (28.8 kW)
Maximum input
GWH450 - 120,000 Btu/h (35.1 kW)
Efficiency in %
Recovery efficiency 82%
Min. Output
GWH450 - 34,200 Btu/h (10 kW)
Temperature Control
Selection range: 100°F (40°C) - 140°F (60°C)
Gas Requirement
Gas connection (inches) - ¾”
Inlet gas pressure under operation (with a high hot
water flow rate)*
• Propane: 11” - 14” water column
• Natural Gas: 5.5” - 8” water column.
* To measure Gas Pressure, see Measuring Gas
Pressure, chapter 3.8.
Venting
3" AL 29-4C Stainless Steel exhaust.
See chapter 3.6 for Venting.
Water
• Hot water connection (inches) - ¾”
• Cold water connection (inches) - ¾”
• Connections:
– Bottom of heater
Combustion
•NOx≤55 ppm
•CO≤250 ppm
•CO
2level (see table 4 for correct restrictor
dimension).
Dimensions
• Depth (in): 11 ¾” (300 mm)
• Width (in): 15 ¾” (400 mm)
• Height (in): 27 ½” (700 mm)
• Weight: 47 pounds (21 kg).
Gas types
Natural Gas.
Liquid Propane.
Converting the gas type can only be done by a certified
gas technician. Call Bosch Water Heating for
conversion information.
Voltage
120 V AC (50/60 Hz)
Amperage
IDLE - 40 mA
Operation - ≤1,5 A
Noise
≤50 db (A)
Safety devices
• Flame failure device (Ionisation flame control)
• Over heat prevention (temperature limiter)
• Pressure switch (exaust protective faulty).
iBOSCH is constantly improving its
products, therefore specifications are
subject to change without prior notice.

6 720 607 915
Appliance details
5
Water resistant
IP X4 (protection against water drops)
2.3 Unpacking the GWH-450-ES heater
This water heater is packed securely.
The box includes:
• Wall-mounted gas water heater
• Bracket and screws for wall hanging the water heater
• Exhaust vent adaptor (with 4 screws and gasket
provided)
• Combustion air inlet adaptor (with 4 screws and
gasket provided)
• Installation manual
• Product registration card
• Energy Guide label
• Safety water pressure valve
• Air deflector
•Restrictors.
Do not lose this manual. Please complete and return
the enclosed product registration card.
Before installing the unit, be certain you have the
correct heater for your type of Gas - Propane or
Natural Gas. Identification labels are found on the
shipping box, and on the rating plate which is located on
the right side panel of the cover.
To remove front cover
BLoosen the two Philips head screws located as
shown in fig. 2.
Fig. 2 Screws
BPull control panel outwards and then pull it
downwards.
Fig. 3 Service position to access water and electric
systems.
BLift front cover panel upward and remove.
The GWH-450-ES is not approved or designed
for:
• Manufactured (mobile) homes, RV's or boats
•Outdoorinstallation
• Combination venting with other appliances.
iThe front cover is secured with two
screws to prevent unauthorized access.
Always secure the control panel and front
cover with these screws.

6 720 607 915
6
Appliance details
2.4 General rules to follow for safe
operation
B1. You should follow these instructions when you
install your water heater. In the United States: The
installation must conform with local codes or, in the
absence of local codes, the National Fuel Gas Code
ANSI Z223.1/NFPA 54.
In Canada: The Installation should conform with
CGA B149.(1,2) INSTALLATION CODES and /or
local installation codes.
B2. Carefully plan where you install the water heater.
Correct combustion air supply and vent pipe
installation are very important. If not installed
correctly, fatal accidents can be caused by lack of air,
carbon monoxide poisoning or fire.
B3. The National Fire Codes do not allow
UNSEALED gas fired water heater installations
in bathrooms, bedrooms or any occupied
rooms normally kept closed. See chapter 3.2
and 3.5.
B4. You must vent your water heater. See section on
VENTING.
B5. The appliance and its gas connection must be leak
tested before placing the appliance in operation.
The appliance must be isolated from the gas supply
piping system by closing its individual manual gas
shutoff valve (not supplied with water heater) during
any pressure testing at pressures in excess of ½ Psig
(3.5 kPa).
B6. Keep water heater area clear and free from
combustibles and flammable liquids. Do not locate
the heater over any material which might burn.
B7. Correct gas pressure is critical for the optimum
operation of this water heater. Gas piping must be
sized to provide the required pressure at the
maximum output of the water heater, while all the
other gas appliances are in operation. Check with
your local gas supplier, and see the section on
connecting the gas supply.
B8. Should overheating occur or the gas supply fail to
shut off, turn off the gas supply at the manual gas
shut off valve, on the gas line. Note: manual gas
shutoff valve is not supplied with the water heater.
B9. Do not use this appliance if any part has been
underwater. Immediately call a qualified service
technician to inspect the appliance and to replace
any part of the control system and any gas control
which has been underwater.
2.5 Cascading function
GWH-450-ES always work as master.
Cascading enables the appliance to be connected in
parallel with up to 4 World 1 appliances. World 1 will
only start, if it gets a signal from the GWH-450-ES and
will (at a defined power output level) give this signal to
the next appliance. That means, the appliance works
always as a Master to the next appliance and always as
a Slave to the one before.
For more detailed information about this feature, consult
the instructions supplied with the accessorie:
• 7 709 003 617.

6 720 607 915
Appliance details
7
2.6 Dimensions and minimum installation clearances
Fig. 4 Dimensions
1Combustion air inlet adapter (right side only)
2Exhaust adapter with CO2measuring point
3Front cover
4On/Off button
5Reset button
6ECO flow thermostat
7LED - (ON) warning light (blinks when in lock out)
8Hot water thermostat
9Mounting plate
Fig. 5 Minimum clearances
Model GWH-450-ES
TOP 12”
FRONT (B) 4”
BACK 0”
SIDES ½”
BOTTOM 12”
VENT DIAMETER 3”
Table 1 Minimum clearances

6 720 607 915
8
Appliance details
2.7 Applications
Introduction
The application designs provided in this manual are general guides to be used when installing this recirculating water
heater. Additional application designs are available from Bosch Water Heating.
Instantaneous water heater (direct tank load version)
Fig. 6
Caution: the water heater which will be
used to supply potable water shall not
be connected to any heating system or
component(s) previously used with a
nonpotable water heating appliance.

6 720 607 915
Installation instructions
9
3 Installation instructions
3.1 Introduction
Please follow these instructions. Failure to follow
instructions may result in:
•Damageorinjury
• Improper operation
• Loss of warranty.
Please contact BBT North America with any questions.
3.2 Proper location for installing your
water heater
Carefully select the location of the water heater. For
your safety and for proper operation, you must provide
combustion air to the water heater and a proper exhaust
vent system.
Follow the guidelines below:
B1. Locate the water heater where venting, gas and
plumbing connections are feasible and convenient.
B2. The hot water lines should be kept short to save
energy. Centrally locating the water heater is best. It
is always best to have hot water lines insulated.
3.3 Water heater placement and
clearances
The GWH-450-ES is design certified for installation on
a combustible wall (see 3.4 Mounting installation)
provided the floor covering below the water heater is
noncombustible. For installations in an alcove or closet,
maintain the minimum clearances to combustible and
non-combustible materials listed below. See also fig. 5.
A. Top 12 inches (305 mm)
B. Front 4 inches (100 mm)
C. Back 0 inches
D. Sides ½ inches (12 mm)
E. Bottom 12 inches (305 mm)
Clearances from any exhaust vent pipe are dependent
upon the clearance requirements of the stainless steel
vent pipe manufacturer. Single wall stainless steel
(AL29-4C) vent pipe (vent type rated for Category III
appliances) must be used when exhaust venting this
appliance. See 3.6 Venting.
3.4 Mounting installation
BSecure the wall mounting bracket provided with the
water heater to a wall surface.
If wall is a stud wall sheathed with plasterboard, it is
recommended that support board(s), either 1x4.s or 1/
2" (minimum) plywood first be attached across a pair of
studs. Then attach the heater’s bracket to the upper
support board. The water heater should be kept level on
the wall surface. See Fig. 7.
Warning: The water in this water
heater is cold and always remains cold
except for the times the burners are on.
In the event of power outage in
conjunction with freezing temperatures,
it is recommended that the heater be
drained. See chapter 5 for draining
instructions.
Warning: Flammable materials,
gasoline, pressurized containers, or any
other items or articles that are potential
fire hazards must NOT be placed on or
adjacent to the water heater. The
appliance area must be kept free of all
combustible materials, gasoline and
other flammable vapors and liquids.
Warning: before starting installation:
Bcheck that there are no loose parts
inside the appliance
Bcheck the gas type of the water heater
matches the gas supply you will be
connecting to the heater.
Bensure that gas pipe, gas valve, fan and
burner have no damage and are proper-
ly fitted.
iFront cover should be removed (see
instructions on page 5) in order to inspect
components visually.
Warning: Do not install this appliance
on a carpeted wall. The water heater
must be mounted on a wall using
appropriate anchoring materials.

6 720 607 915
10
Installation instructions
Fig. 7 Mounting the water heater
3.5 Combustion air requirements
Twin pipe
The GWH-450-ES is designed as a sealed combustion
appliance. It is recommended that the combustion air
be provided by a dedicated 3” pipe to the outside. The
combustion air pipe may be constructed of aluminum
flex, PVC or any other rigid or semi rigid sealed 18 inch.
The combustion air inlet should be located in such a
manner as to provide a 3 foot clearance from the
exhaust vent terminator. See Fig. 18 Letter I.
The maximum length of the combustion air inlet is 39
feet with one elbow. Subtract 6feet for additional
elbows. Maximum number of elbows permitted is 4.
Single pipe
Although it is permissible to draw combustion air from
the inside, it is not the manufacturer’s recommended
installation method. Always install a 3 inch elbow on the
top right side of the combustion air inlet to prevent
foreign object from falling into the unit (see Fig. 17).
If a single pipe installation is performed. Use the
following guidelines when providing adequate
combustion air for the recirculating water heater as well
as any other appliances that may consume air in the
space. Always follow local codes if more stringent.
•Appliances located in unconfined spaces:
–a) An unconfined space is one whose volume is
greater than 50 cubic feet (1.42 cubic meter) per
1000 Btu per hour (292.81 Watts) of the
combined rating of all appliances installed in the
space. That would be 6200 cubic feet (175.6
cubic meter) for the GWH-450-ES alone.
–b) In unconfined spaces in buildings of
conventional frame, masonry, or metal
construction, infiltration air is normally adequate to
provide air for combustion.
•Appliances located in confined spaces:
The confined space must be provided with two per-
manent openings, one commencing within 12 inches
(304.8mm) of the top and one commencing within
12 inches (304.8mm) of the bottom of the enclosure.
Each opening must have a minimum free area of one
square inch per:
– 1000 Btu/hr (292.81 Watts) if all air is taken from
inside the building
– 2000 Btu/hr (585.62 Watts) if all air is taken from
the outside by horizontal ducts
– 4000 Btu/hr (1171.24 Watts)if all air is taken from
the outside by direct openings.
Or the confined space must be provided with one
permanent opening or duct that is within 12 inches
(304.8mm) of the ceiling of the enclosure. This opening
must have a minimum free area of one square inch per:
– 3000 Btu/hr (878.43 Watts) if all air is taken from
the outside by a direct opening.
Louvers, grills and screens have a blocking effect, when
used, increase the sizes of your openings by 400% for
wood louvers (as wood type will reduce the free air by
75%) and 135% for metal louvers (as metal will reduce
the free air by 30%). Refer to the National Fuel Gas
Code for complete information. In buildings of tight
construction all air should be taken from outside.
Warning: In areas where freezing
temperatures are common the twin pipe
system is recommended. A negative air
condition may result in cold air being
drawn across the heat exchanger coil
causing it to freeze and burst. This
failure is not covered under the
manufactures warranty.
Warning: When installed in an
environment where corrosive chemicals
or dirty air are present the twin pipe
system is required.

6 720 607 915
Installation instructions
11
3.6 Venting
Establish vent clearances that comply with the vent
manufacturer's specifications. In all cases follow local
codes. See Table 3.
The appliance should be located as close to the point
of termination as possible. The maximum vent length is
39 feet (12 m) with one 90 degree elbow. Subtract 6
feet from the total vent length for each additional 90°
elbow used (a maximum of four 90° elbows are
permitted in the total vent length), or subtract 3feet for
every 45° elbow used. Horizontal sections of vent must
pitch ¼" for every foot of horizontal length, to prevent
the pooling of condensate, and be supported at 4 foot
intervals with overhead hangers.
Note: Listed thimbles or collars are necessary to pass
through wall and ceiling partitions. If the vent system
passes through combustible areas where the vent
clearance requirements cannot be maintained, it is
permissible to chase straight sections of sealed 3 inch
single wall vent through 4 inch (or greater) Type-B vent.
The distance to combustibles using this chase
technique is 1 inch. Note: Type-B vent should never
be used as the actual exhaust vent system for the
appliance, as it is not gas tight.
Minimum exhaust vent size and length
Fig. 8
Maximum exhaust vent and combustion air inlet
lengths
Fig. 9
Note: reduce 6ft for each 90° elbow used after the first
one, reduce 3ft for each 45° elbow.
Exhaust vent conditions
Warning: Do not reduce the vent
(exhaust and combustion) pipe sizes
and do not common vent with any other
vented appliance or stove.
Warning: Failure to vent the exhaust
gases to the outside with sealed
stainless steel vent pipe (AL29-4C)
may result in dangerous flue gases
filling the space in which it is installed.
Warning: Do not mix vent pipe or
joining methods from different
manufactures.
Z flex Protech Heat Fab
3” VENTING
3” Horizontal
Terminal
TEE
Only
TEE Only 9390 TEE
Table 2 Terminals/Adapters Part Numbers
Caution: The vent system must be
installed by a qualified agency in
accordance with these instructions. If
improperly installed a hazardous
condition such as explosion or Carbon
Monoxide poisoning could result.
Bosch Water Heating will not be
responsible for improperly installed
appliances.
Diam. Max
length
Material
Exhaust
Vent
3 inches 39 feet
with 1
elbow
Sealed stainless
steel (AL29-4C)
Intake
Vent
3 inches 39 feet
with 1
elbow
Aluminum flex,
PVC or any other
rigid or semi rigid
sealed 3 pipe
Table 3 Venting Specifications
Caution: Any horizontal flue system
fitted to the appliance must incline
towards the appliance at an angle of
3% to prevente condensate dripping
from the flue terminal.
The minimum exhaust vent length is
3 feet.
The use of a 90 degree elbow is
equivalent to 6ft in vent length.
The use of 45 degree elbow is
equivalent to 3ft in vent length.

6 720 607 915
12
Installation instructions
Fig. 10 Side vent
Fig. 11 Rear vent
Vent Safety System
The GWH-345/450-ESR will shut down if inadequate
exhaust venting is detected or a lack of combustion air
is provided to the unit; see troubleshooting section on
page 24. See error code to confirm error, correct the
problem and then reset the heater before operating.
Attaching the exhaust and air inlet connection
adaptors to the top of the heater
Fig. 12 Mounting sequence
Fig. 13 Exhaust
Fig. 14 Air inlet
BAttach the flue gas exhaust accessory (8 705 504
142) to the top of the unit (position 1) using the 4
screws and gasket provided, and fully insert 3"
stainless steel vent pipe into the accessory and
tighten the clamp (position 2).
BPlace first gasket into fresh air intake.
BPlace air deflector.
BPlace second gasket and then the restrictor on top of
deflector (use table 4 for the correct side).
BAttach the combustion air inlet accessory (8 705
504 141) to the top of the unit (position 3) using the
4 screws and gasket provided, and fully insert 3"
combustion air pipe into the accessory and tighten
the clamp (position 4). NOTE: The appliance has the
possibility to mount the combustion air inlet
accessory only on the top right side of the heater.
The left side must be kept sealed.

6 720 607 915
Installation instructions
13
Restrictor definition
Use table below to define which restrictor to be used.
Selecting a restrictor (sample)
Use table below to define which restrictor to be used.
In above example, total equivalent length is 63 feets.
Using table 4 we conclude that the restrictor to be used
is:
• GWH450ES NG - restrictor 50
• GWH450ES LPG - restrictor 55.
Total equivalent
length (ft)
Restrictor
Ø
GWH450 NG
18 -28 44
28 -40 47
40 -65 50
65 -100 55
GWH450 LPG
18 -28 47
28 -50 50
50 -75 55
75 -100 60
Table 4 Restrictors
iDescribed example was done taking as
example Fig. 15.
Part 3 feet 1 foot 90° 45° out/in Total equivalent
length
Comb, gas steel
Number of
parts
10 ----- 1 ----- 1
48.0
Equivalent
length/part
3.0 1.0 6.0 3.0 12.0
Total equivalent
length/part
30.0 ----- 6.0 ----- 12.0
Comb, gas steel
Number of
parts
6 ----- 1 ----- 1
15.0
Equivalent
length/part
1.5 0.5 3.0 1.5 3.0
Total equivalent
length/part
9.0 ----- 3.0 ----- 3.0
Part 4 feet 1 foot 90° ----- -----
Fresh air PVC
Number of
parts
----- ----- ----- ----- -----
0
Equivalent
length/part
2.0 0.5 1.0 ----- -----
Total equivalent
length/part
----- ----- ----- ----- -----
Total: 63
Table 5 Selecting a restrictor
iAbove table should be used to define the
correct restrictor for each type of
installation.

6 720 607 915
14
Installation instructions
3.6.1 Venting options
Installing this water heater as a room sealed (TWIN
PIPE SYSTEM) is the recommended method. Contact
Bosch Water Heating or dealer for available vent
termination kits and vent materials for this water heater.
Room sealed installation (TWIN PIPE SYSTEM)
Fig. 15
Combustion air pipe: ≤39 ft (12 m)
Exhaust vent pipe: ≤39 ft (12 m)
Fig. 16
Combustion air pipe: ≤39 ft (12 m)
Note: reduce 6ft for each 90° elbow used after the first
one, reduce 3ft for each 45° elbow.
A maximum of four 90-degree elbows are permitted in
both the exhaust and combustion air vent lengths.
Open combustion installation (SINGLE PIPE
SYSTEM)
Not recommended in cold climate areas, see
Chapter 3.5.
Fig. 17
Exhaust vent pipe: ≤39 ft (12 m)
The exhaust vent system must vent directly to the
outside of the building and an adequate amount of
indoor combustion air must be provided for this
installation. See chapter 3.5.
Connecting a one piece 90 degree elbow pipe to the
combustion air inlet adaptor is necessary, this will
prevent debris or objects from ever falling into the inlet
opening.
Note: reduce 6ft for each 90° elbow used after the first
one, reduce 3ft for each 45° elbow.
A maximum of three 90-degree elbows are permitted.

6 720 607 915
Installation instructions
15
Recommended exhaust vent terminator position
Fig. 18
* Subject to local codes and anticipated snow level
** Other equipment that operates with a mechanical air inlet may require greater distances, reference manufacturer's instructions
Ref. Description Minimum distance
ADirectly below an opening; operable windows, doors and any non-
mechanical fresh air openings
12 in (twin pipe installation)
48 in (single pipe installation)
B
Below a gutter, sanitary pipework or eaves 24 in
Below a gutter, sanitary pipework or eaves, protected by metal
shielding 12 in
CFrom any internal corner 12 in
D* Above ground or snow pack 12 in
Above a paved sidewalk 7 ft
EFrom an opposing wall or structure facing the termination 24 in
From the relief valve of a Ip gas regulator 36 in
FFrom a terminator facing a terminator 48 in
GVertically between two exhaust vent terminators on the same wall 60 in
HHorizontally between two exhaust vent terminators on the same wall 12 in
I**
Horizontally and vertically from combustion air inlet of a two system
GWH-450-ES 18 in
From the gravity combustion air inlet any other equipment 48 in
JFrom any external corner 12 in
KHorizontally from an opening; operable windows, doors and any non-
mechanical fresh air openings 12 in
LFrom wall on exhaust applications 10 in
Table 6

6 720 607 915
16
Installation instructions
Supporting the exhaust vent system
Fig. 19 Horizontal side wall venting installation
(combustion air piping not being shown)
Note: Pitch vent away from heater
3.7 Gas piping & connections
Before connecting the gas supply, check the rating
plate on the right side of the heater to be sure that the
heater is rated for the same gas to which it will be
connected.
In the United States: The installation must conform with
local codes or, in the absence of local codes, the
National Fuel Gas Code ANSI Z223.1/NFPA 54.
In Canada: The Installation should conform to CGA
B149 INSTALLATION CODES and/or local installation
codes.
GAS CONNECTIONS
BInstall a manual gas shut off valve, on the gas supply
line.
BInstall a union when connecting gas supply.
BThe minimum diameter required for any appliance
connector used is ¾”.
BNational Fuel Gas Code requires that a sediment
trap (drip leg) be installed on gas appliances not so
equipped. The drip leg must be accessible and not
subject to freezing conditions. Install in accordance
with the recommendations of the serving gas
supplier.
When connections are made, check for gas leaks at all
joints. Apply some gas leak detection solution to all gas
fittings. Bubbles are a sign of a leak. A combustible gas
detector may also be used to detect for leaks.
GAS LINE SIZING
The gas supply piping should be sized according to the
applicable code for a maximum draw of 120,000 BTUH.
Measure the length of gas supply line and use the tables
in Fig. 21 or the gas line manufacturer’s sizing tables to
determine the pipe diameter necessary to
accommodate the BTU demand of the unit. If there are
more gas drawing appliances on the line, size the gas
line according to the total maximum amount of BTU
draw for all appliances.
Note: Under sizing the gas line may result in diminished
output and improper operation. See chapter 3.8 for the
procedure to confirm gas pressure.
Fig. 20
Warning: DO NOT connect to an
unregulated or high pressure propane
line or to a high pressure commercial
natural gas line.
Warning: The water heater must be
isolated from the gas supply piping
system during any pressure testing of
that system at test pressures equal to or
more than 0.5 psig. If overpressure has
occurred, such as through improper
testing of the gas lines or malfunction of
the supply system, the gas valve must
be checked for safe operation.
Danger: If you have a leak, shut off the
gas. Tighten appropriate fittings to stop
leak. Turn the gas on and check again
with a gas leak detection solution.
Never test for gas leaks using a match
or flame.
Gas piping Inlet gas particle screen

6 720 607 915
Installation instructions
17
FOR NATURAL GAS
Maximum Capacity of pipe in Cubic Feet of Gas per Hour for Gas Pressure of 0.5 Psig or less and a Pressure drop
of 0.3 in Water Column (0.75mbar).(Based on a 0.60 Specific Gravity Gas) Btu numbers given in thousands.
Fig. 21
Follow boxed numbers for piping just one GWH-345/450-ESR (example: ¾” B.I. Natural Gas pipe for 20 ft
(6.1m). will handle 190,000 btu’s (55.7 kWh). For multiple appliances combine the total btu input load and
then refer to applicable chart below.
Nominal
Iron Length of Black Iron Pipe, Feet
Pipe Internal
Size, Diameter
inches inches 10 20 30 40 50 60 70 80 90 100 125 150 175 200
1/4 0.364 32 22 18 15 14 12 11 11 10 9 8 8 7 6
3/8 0.493 72 49 40 34 30 27 25 23 22 21 18 17 15 14
1/2 0.622 132 92 73 63 56 50 46 43 40 38 34 31 28 26
3/4 0.824 278 190 152 130 115 105 96 90 84 79 72 64 59 55
1 1.049 520 350 285 245 215 195 180 170 160 150 130 120 110 100
1 1/4 1.380 1050 730 590 500 440 400 370 350 320 305 275 250 225 210
1 1/2 1.610 1600 1100 890 760 670 610 560 530 490 460 410 380 350 320
2 2.067 3050 2100 1650 1450 1270 1150 1050 990 930 870 780 710 650 610
* EHD = Equivalent Hydraulic Diameter. The greater the
value of EHD, the greater the gas capacity of the tubing.
Maximum Capacity of Semi-Rigid (flexible, non
corrugated) Tubing in Thousands of BTU per Hour of
Undiluted Liquefied Petroleum Gases (at 11 inches
Water Column Inlet Pressure).
(Based on a Pressure Drop of 0.5 Inch Water Column)
* Source National Fuel Gas Code NFPA 54, ANSI
Z223.1 - No Additional Allowance is necessary for an
ordinary number of fittings
FOR LP GAS
Maximum Capacity of Pipe in Thousands of BTU per Hour of Undiluted Petroleum Gases (at 11 inches Water Column Inlet
Pressure) (Based on a Pressure Drop of 0.5 Inch Water Column).
Copper
Outside Length of Tubing, Feet
diameter
Inch 10 20 30 40 50 60 70 80 90 100
3/8 39 26 21 19 _ _____
1/2 9262 50 41 37 3531292726
5/8 199 131 107 90 79 72 67 62 59 55
3/4 329 216 181 145 131 121 112 104 95 90
* EHD = Equivalent Hydraulic Diameter. The greater the
value of EHD, the greater the gas capacity of the tubing.
Tube
size,
inches EHD*
10 20 30 40 50 60
1/2 18 EHD 82 58 47 41 37 34
3/4 23 EHD 161 116 96 83 75 68
1 30 EHD 330 231 188 162 144 131
1 1/4 37 EHD 639 456 374 325 292 267
Length of Flexible Corrugated Stainless Steel Tubing (CSST), Feet
Tube
size
inches EHD*
10 20 30 40 50 60
1/2 18 EH
D
129 91 74 64 58 53
3/4 23 EH
D
254 183 151 131 118 107
1 30 EH
D
521 365 297 256 227 207
1 1/4 37 EH
D
971 661 528 449 397 359
Length of Flexible Corrugated Stainless Steel Tubing (CSST), Feet
Nominal
iron Black Iron Pipe
pipe Length of Pipe, Feet
Inches 10 20 30 40 50 60 80 100 125 150 200
1/2 291 200 160 137 122 110 94 84 74 67 58
3/4 608 418 336 287 255 231 197 175 155 140 120
1 1145 787 632 541 480 434 372 330 292 265 227

6 720 607 915
18
Installation instructions
National Fuel Gas Code requires that a sediment trap
(drip leg) be installed on gas appliances not so
equipped. Also, a manual gas shut off valve must be
installed on the gas supply line within close proximity of
the water heater and be visible from the water heater.
The water heater must not be piped with gas supply
pressures in excess of 0.5 psig. If overpressure has
occurred, such as through improper testing of the gas
lines or malfunction of the supply system, the gas valve
must be checked for safe operation.
When connections are made, check for gas leaks at all
joints. Apply some soapy water to all gas fittings. Soap
bubbles are a sign of a leak.
3.8 Measuring gas pressure
Connecting manometer
BTurn power off.
BShut off gas supply.
BRemove front cover and locate the inlet gas
measuring point (see Fig. 22).
BLoosen screw inside test point fitting (do not remove)
and connect manometer tube on test point.
Fig. 22 Gas pressure measuring (lower tapping)
Static pressure test
BTurn gas supply on.
BOperate all other gas appliances on same gas piping
system at maximum output.
BRecord static pressure reading in table 7.
Operating pressure test
BPress On/Off button to turn heater On.
BAfter 10 seconds, press and hold the reset button
.
BRotate the recirculating water temperature selector
(left knob) to the minimum and then to maximum.
BRelease the reset button and the display should
show * blinking.
BPlace a demand for heat by turning thermostat
control to maximum.
BRecord operating pressure reading in table 7.
Operating gas pressures lower than 5" W.C. for natural
gas or 11" W.C. for LP will result in improper operation
and must be corrected. See Chapter 3.7 for gas line
sizing requirements.
Warning: The water heater must be
disconnected from the gas supply
piping system during any pressure
testing of that system at test pressures
equal to or more than 0.5 psig.
Danger: If you have a leak, shut off the
gas. Tighten appropriate fittings to stop
leak. Turn the gas on and check again
with a soapy solution. Never test for gas
leaks using a match or flame.
iNote: after verification tight the screw
inside the test point.
Static Gas Pressure Reading (see Chapter 3.8)
enter here: ___________________
Operating Gas Pressure Reading (see Chapter 3.8)
enter here: ___________________
Table 7

6 720 607 915
Installation instructions
19
3.9 Water connections
BWhen facing the water heater, the ¾” return is on the
bottom right and the supply is on the bottom left.
Install the heater centrally in the building if possible
and make piping runs as short as possible.
Fig. 23
BThe use of a union when connecting both water
pipes to the return and supply connections are
recommended, this will facilitate any necessary
servicing.
BAlthough water piping throughout the building may
be other than copper, we recommend that copper or
suitably rated stainless steel flex line piping be used
for the water connections for 1.5’ on either side of
the water heater (follow local codes if more
stringent).
BNever sweat any rigid piping directly to or beneath
the water connections, damage can occur to the
internal parts of the heater from heating of the pipe.
BPlastics or other PEX type plumbing line materials
are not suitable for connecting directly to the water
heater.
BKeep water inlet and outlet pipes to no less than ¾"
(19.05mm) diameter to allow the full flow capacity.
BIf the cold and hot connections to the heater are
reversed, the water heater will not function. Be
certain there are no loose particles or dirt in the
piping. Blow out or flush the lines before connecting
to the water heater.
BFull port valves should be installed on both the cold
water supply and hot water outlet lines to facilitate
servicing the water heater (see Fig. 24).
BFor installation on a private well system with the use
of a pressure tank, the lowest pressure range setting
recommended is 30-50 psi (2.07 and 3.45bar).
Connecting the pressure relief valve (PRV)
A listed pressure relief valve supplied with the heater
must be installed at the time of installation. No valve is
to be placed between the PRV and the water heater. No
reducing coupling or other restriction may be installed
in the discharge line. The discharge line must be a
minimum of 4” above a drain and installed such that it
allows complete drainage of both the PRV and the line.
The location of the PRV must be readily accessible for
servicing or replacement, and be mounted as close to
the water heater as possible. See Fig. 24. To install the
PRV, a suitable fitting connected to an extension on a
“T” fitting can be sweated to the hot water line.
Support all piping.
Fig. 24 Plumbing Connections and Pressure Relief
Valve
3.10 Electrical connections
The GWH-450-ES requires an electrical power supply
from a 120VAC 60Hz circuit and must be properly
grounded.
A means for switching off the 120VAC power supply
must be provided.
The heater is wired as shown in the wiring diagram
(chapter 4.7, Fig. 29).
HOT COLD
Warning: For safety reasons,
disconnect the power supply to the
heater before any service or testing is
performed.
Warning: This water heater must be
electrically grounded in accordance
with the most recent edition of the
National Electrical Code. NFPA 70. In
Canada, all electrical wiring to the
heater should be in accordance with
local codes and the Canadian Electrical
Code, CSA C22.1 Part 1. Do not rely
on the gas or water piping to ground the
metal parts of the water heater.

6 720 607 915
20
Operating instructions
4 Operating instructions
Before proceeding with the operation of the water
heater make sure that the system is filled with water:
BTurn off power supply to water heater.
BOpen the cold water inlet supply to the water heater
fully.
BOpen a hot water faucet to permit the water to fill the
water heater and the piping and to eliminate the air
trapped in the system.
BClose the hot water faucet after the water flows freely
and all the air has escaped from the system. Turn on
power supply to heater. The water heater is now
ready to operate.
Fig. 25
4On/Off switch
5Reset button
6ECO flow selector
7LED - (ON) warning light (blinks when appliance in lock out)
8Hot water temperature selector
10 LED to display error codes and temperatures
4.1 For your safety read before
operating your water heater
WHAT TO DO IF YOU SMELL GAS
BDo not try to operate any appliance.
BDo not touch any electric switch; do not use any
phone in your building.
BImmediately call your gas supplier from a neighbors
phone. Follow the gas supplier’s instructions.
BIf you cannot reach your gas supplier, call the fire
department.
BUse only your hand to press the on/off control switch.
Never use tools. Follow these instructions exactly. If
control switch is jammed, close the gas supply and
call a qualified service technician. Attempted forceful
repair may result in a fire or explosion.
BDo not use this appliance if any part has been under
water. Immediately call a qualified service technician
to inspect the appliance and to replace any part of
the control system and any gas control which has
been under water.
4.2 Startup instructions
B1. STOP! Read the previous safety information.
B2. The gas valve must be shut off by putting the ON/
OFF switch to position OFF. Wait five (5) minutes to
clear out any gas. If you smell gas, STOP! Follow “B”
in the safety information above. If you do not smell
gas, go to the next step.
B3. This appliance is equipped with electronic ignition
for lighting the main burners. When turning the water
heater on, follow these instructions exactly.
B4. Press the ON/OFF switch to the ON position. In
this position, the water heater is ready to use.
B5. Close the TT (thermostat) connection to activate
heater.
B6. The burners will remain on until the heat demand
is met.
When the water heater is in operation you will hear its
power vent fan and burner operating. After a call for
heat, the power vent fan will continue to operate for up
to 60 seconds to exhaust all flue gases.
TO TURN OFF GAS TO APPLIANCE
BTurn off the manual gas shut off on the supply line to
the water heater and set the ON/OFF switch to the
OFF) position. Note: a manual gas shut off valve is
not supplied with the water heater.
Warning: If you do not follow these
instructions exactly, a fire or explosion
may result causing property damage,
personal injury or loss of life.
iNOTE: upon installation or after
gas line work has been done, air
in the gas line may cause a
lockout error. Reset the unit
(Fig. 25, pos. 52). The water heater
will reattempt ignition.